Ruslan Pukhov, director of the centre for analysis of strategies and technologies, a defence thinktank in Moscow, said: “They [the Chinese] are trying to copy this system illegally. They’ve already copied a whole series of our weapons.

“They’re trying to clone the S-300, to serve their interests and also to export. As I understand it, it’s not all working out. They probably wanted extra documentation to better deal with this task of reverse engineering.”

A report by the Stockholm International Peace Research Institute (Sipri) released this week warned that the Sino-Russian relationship was growing increasingly uneasy given China’s international rise.

“In the coming years, while relations will remain close at the diplomatic level, the two cornerstones of the partnership over the past two decades – military and energy co-operation – are crumbling,” the thinktank wrote. “As a result, Russia’s significance to China will continue to diminish.”